The theory of chronic deafferentation dysesthesias

The chronic dysesthesias are abnormal disturbing somatic sensations, which are painful or non-painful. Their abnormality is revealed by their null or distorted psychophysical relationships; they occur spontaneously or can be peripherally induced by innocuous or noxious stimuli. Among nonverbal or mentally incompetent humans and also subhumans, these dysesthesias are expressed by patterns of escape or avoidance behaviors. There is no contemporaneous and necessary relationship with peripheral nociception. The basic mechanisms of these abnormalities have been obscure, and conventional modes of therapy have been unsuccessful. The origin of these chronic abnormalities is known to arise from lesions of peripheral or central components of the neural pathway for normal pain and temperature sensibility. The cause of these abnormalities is thought to reside in pathophysiological foci of excitability among deafferented central nocireceptive neurons. The spontaneous dysesthesias can occur after partial or total deafferentation. The peripherally induced dysesthesias occur after partial deafferentations, which include loss of small caliber myelinated afferents in cases of peripheral origin; and they are mediated via remaining afferent pathways. Little is known about the deafferented neurons in the brain, or the pertinent remaining central afferent pathways. More is now known about the pathophysiological effects of deafferentation on nonspecific nocireceptive neurons in the dorsal horn. These include morphological alterations, reduced inhibition, supersensitivity, hyperexcitability, and novel afferent excitation. Additional studies of chronic deafferentation in subhumans are necessary to provide further information and to test hypotheses concerning the chronic deafferentation dysesthesias.